Method for producing resin treated leather



METHOD FOR PRODUCING RESIN TREATED LEATHER John W. Cunningham, SanAntonio, and Robert S. Singleton, Blanco, Tex., and George W. Singleton,Greenville, S.C., assignors to Lucille V. Singleton, doing business asRussell A. Singleton & Sons, Blanco, Tex.

No Drawing. Application October 22, 1952 Serial No. 316,314

8 Claims. (Cl. 117-7) This invention relates to new and usefulimprovements in resin treated leather and methods for producing suchleather. p

The invention is concerned with the production of treated leather havingincreased abrasion resistance While retaining the various naturalattributes of leather virtually unchanged. Manifestly, such leather hasmany and varied uses. For the purpose of simplicity, however, theinvention will be described in conjunction with the use of the treatedleather in the textile industry.

In the branches of the textile industry concerned with the handling ofvarious textile yarns, and in particular, with the spinning of suchyarns, there are various instances in which the yarn is passed incontact with leather belts or leather rollers. While leather serves verywell in such instances and provides beneficial results, it has certainshortcomings, such as a lack of resistance to abrasion, and some effortshave been made to replace the leather with other materials such asreinforced rubber or various synthetics.

A particular point at which trouble has been experienced has been inspinning frames which employ long draft spinning aprons as well ascovered rollers known as spinning cots. During the spinning operation,the spinning aprons are driven by relatively small rollers which may beknurled, fluted, etched or otherwise provided with an uneven orroughened surface, and also pass over and around stationary metal barsat a relatively sharp angle. The driving roller and the metal bar comein contact with the inner side of the apron, which is in the form of asmall endless belt, this inner side being the flesh side in the case ofa leather apron. Obviously, the wear and abrasion on the inner side ofthe apron is severe. The outer surfaces of the aprons, which in the caseof leather aprons is the grain side, engage the yarn being processed andfurther receive considerable abrasion and wear from such yarn.

Leather is the most desirable material presently known for use inspinning aprons and, by and large, produces better yarn. The leatherbelts are more uniform in thickness, produce yarn of better qualitybecause of the cushioning effect of the leather and because of thegripping power of the leather grain surface. Further, leather is oilabsorbent so as to prevent the accumulation of any oil upon the surfaceof the apron, and leather belts may be spliced in place upon thespinning frame so as not to require disassembly of the frames forreplacement of the aprons.

None of the foregoing is true of the various synthetic or rubber longdraft spinning aprons which have been developed and which are in use,but the latter have the advantage of greater abrasion resistance uponboth their inner and outer surfaces. Synthetic aprons often break due toan accumulation of lint or yarn upon the roller over which the apron orbelt passes, but in general, have a longer useful life than ordinaryleather aprons because of their greater toughness and abrasionresistance. They have replaced ordinary leather aprons to some extentUnited States Patent because of their lower cost and because they causeless trouble due to stretching.

Thus, both of the presently available types of spinningaprons havecertain advantages and disadvantages, but no apron or belt is availablewhich combines the desirable features of both the synthetic and leatheraprons and at the same time avoids their undesirable points.

The foregoing disadvantages of ordinary leather have.

an adverse effect upon its use in other fields than the textile industryand either shorten the useful life of the leather, or discourage itsuse. The natural pliability, resilience and elasticity of leather, alongwith its feel or appearance, and other well-known attributes, have notbeen completely duplicated in other materials, such as the synthetics,and yet the shortcomings of leather as to;

insufiicient abrasion resistance, surface cracking and the like, remainas objectionable characteristics of conventional leather.

It is, therefore, one object of this invention to provide an improvedtreated leather which has all of the desirable features of conventionalleather, and in addition, has increased toughness and abrasionresistance which greatly enhance the useful life of the leather.

A particular object of the invention is to provide an improved longdraft spinning apron formed of leather properly treated with a resin toincrease the toughness and abrasion resistance of the leather throughoutits thickness.

Yet another object of the invention is to provide an improved apron ofthe character described in which the inherent characteristics of thenatural leather are retained, and in particular, wherein the oilabsorbency of the leather is retained to a large degree.

An additional object of the invention is to provide an improved methodfor treating leather with resins to increase the abrasion resistance ofthe leather, the method being applicable to both vegetable-tannedleather and chrome-tanned leather.

One objection to ordinary leather draft aprons is the tendency of theleather to wear unevenly because of hard and soft spots in the leather.The invention by suitably impregnating the leather with a resinovercomes this difficulty and causes the apron to wear evenly anduniformly.

Another objection of ordinary leather draft aprons has been theirtendency to develop surface cracks which nip or pinch the yarn as theapron is flexed. This action results in uneven yarns and, hence, isundesirable. The apron produced by this invention is resistant tocracking on the outer or skin side as well as abrasive wear on the inneror flesh side.

A further object of the invention is to provide an improved method forimpregnating leather with resin wherein excessive shrinking and/orplumping of the leather is avoided or minimized.

Still another object of the invention is to provide an improved methodfor the impregnation of leather with resin wherein controlled drying ofthe leather after impregnation permits control of the shrinking orplumping of the leather.

A particular object of the invention is to provide a resin-treatedleather long draft spinning apron which will wear much longer than anordinary leather apron, and which retains all of the advantageouscharacteristics of ordinary leather aprons while avoiding thedisadvantages thereof and while achieving substantially all of thebeneficial characteristics of rubber or synthetic aprons.

' Methods of carrying out the invention will be herein.- after describedas well as the nature and structure of the improved leather producedthereby.

Various other objectives and features of the invention will appear morefully from a reading of the following Patented May 5, 1959.

specification wherein examples of the invention and the methods thereininvolved are described.

In carrying out the invention, the leather, which may bevegetable-tanned or chrome-tanned, is impregnated with a stu'table waterdispersion of a resin selected from the group of resins which areinherently flexible, oil resistant, abrasion resistant, and subject todispersion in an aqueous medium. The resin should be thermo-plastic andshould be capable of being made flexible without the use of mobileplasticizers which are subject to selective absorption by leather.

Saturation of the leather can be obtained by brushing, spraying, orroller coating the flesh side of the leather or by total immersion ofthe leather in the water dispersion of the resin. It has been found thattotal immersion is preferable, but any of the methods of resinsaturation should be followed by removal of the excess resin by passingthe leather through squeeze rollers or by subjecting the leather tocentrifugal action.

Following saturation of the leather with the resin, the leather is driedslowly, desirably in an atmosphere of controlled humidity in order tominimize shrinkage and/ or plumping of the leather. Vegetable-tannedleather tends to plump following the resin treatment, whilechrome-tanned leather tends to shrink both in length and width. Sincelong draft spinning aprons of the best quality must conform torelatively small tolerances of the magnitude of a few thousandths of aninch, the thickness of the leather, when it is to be used for spinningaprons, must be carefully controlled and maintained throughout thistreating process.

When the treated leather has been properly dried, it is desirablysubmitted to a resin fusing step in which the leather is subjected to anelevated temperature for a short period of time, desirably underpressure, to fuse or weld the deposited resin. Because of the nature ofthe resin impregnation steps employed, the pores and interstitial spacesof the leather are not completely filled with resin, but instead, theresin apparently is deposited at the intersections and points ofcontinuity of the leather fibers so that the fusing or curing processresults in the bonding of the leather fibers to one another at amultitude of spaced points.

Hence, the leather is reinforced, not by a continuous resin film orbody, but rather, by a multiplicity of closely spaced but separatedresin bodies of minute size. The resulting resin reinforced leather isbelieved to be novel in that the oil absorbency and other normalcharacteristics of the leather are not materially reduced, and extremeflexing of the treated leather does not result in destruction of thebond between the resin and the leather or mechanical destruction of theminute bodies of resin.

While the desired long draft spinning aprons reasonably could be formedfrom the leather following treatment, it is preferable to cut theleather to the desired width and thickness prior to the treating processso that, following the treatment, the leather requires no additionalprocessing other than cutting into proper lengths and preparation forthe joining of the ends of each length to form an endless long draftspinning apron.

The treated leather displays qualities comparable to those of untreatedleather, and in addition, overcomes some of the undesirablecharacteristics of untreated leather. The oil absorbency of the treatedleather is retained along with the natural cushioning effect of theleather and the inherent gripping power of the grained surface. On theother hand, the tendency of leather to develop surface cracks iseliminated, and stretching of the leather is reduced. At the same time,the treated leather has much greater toughness and abrasion resistancethan the untreated leather and is fully equivalent if not superior torubber or synthetic material in this respect.

Both chrome-tanned and vegetable-tanned leather, treated and untreated,have been tested for abrasion resistance with a standard Taber abraser,providing the following results, each figure representing the average offive individual tests. Treated and untreated samples were cut fromadjacent portions of the same hides to insure comparability:

Comparative abrasion resistance Number of Wear-Cycles Loss in ThicknessChrome-Tanned Vegetable-Tanned Treated Un- Treated Untreated treated Theabove results show a significant increase in flat abrasion resistance asa result of the resin treatment. A much greater increase in wear lifewas observed, however, when flexure was included in the test by placingtreated and untreated leather aprons in actual use in a spinning mill.While all of the tests in actual commercial use have not yet beencompleted due to inability to produce failure of treated aprons in orderto define the useful life of the same, the results of one test may begiven.

In a spinning frame handling number ten rayon, which is very damaging toordinary leather aprons, a number of ordinary leather bottom aprons wereinstalled and an equal number of treated leather bottom aprons. In afour month period, two of the untreated leather aprons had to bereplaced, and measurement of the thickness of the aprons disclosed thatthe treated aprons showed no'wear while the untreated aprons had alreadylost about onehalf of their useful life.

In addition, both the abraser and the spinning frame tests disclosedthat the untreated leather wore unevenly because of the hard and softspots inherently present in the leather. The treated leather wore evenlyin both cases, this being attributed to a greater concentration of resinin the soft areas of the leather due to such areas taking up more resinduring the treating process.

The uneven wear of aprons is very undesirable in that it adverselyaffects the quality and uniformity of the yarn being spun, and thiselimination of uneven wear is thought to be quite novel as well asbeneficial.

The treated aprons displayed marked abrasion resistance on their fleshside, and showed no tendency to develop surface cracks upon their skinsides. The extent of the useful life of the treated apron has not yetbeen determined because of inability to date to wear out or destroy thetreated aprons in commercial use.

The tests upon the Taber abraser were quite beneficial in determiningthe qualities of the treated and untreated leather. A sample ofuntreated leather subjected to 3000 wear cycles was worn down of aninch, the leather fibers were torn and distorted, and the wear was veryuneven. As much as $1000 of an inch variance in wear was observed.

A treated sample of leather subjected to 3000 wear cycles was worn X ofan inch, the wear was even, and the leather fibers were not torn ordistorted.

The most desirable resin yet found for treating the leather is a waterdispersion of polyvinyl chloride, preferably plasticized with abutadiene-acrylonitrile copolymer. Increasing thebutadiene-acrylonitrile content reduces the abrasion resistance of theapron but increases the flexibility thereof. Specifically, optimumproperties for improved long draft spinning aprons are exhibited by atreated leather containing from 2% to 6% resin de- Total solids percent45-50 pH i 8-9 Surface tension (dynes/cm.) 35-42 Viscosity (centipoises)10-20 Particle size (microns) 0.25 Specific gravity (latex) 1.08

The compositions and methods of preparation of suit able resindispersions, as described hereinabove, are set forth in the patent toWheelock, No. 2,614,094, issued October 14, 1952.

Various other resins have proved usable including the acrylic,butadiene-styrene, vinyl butyral, and styrene polymers. In addition tothe polyvinyl chloride, the polystyrenes and the polyvinyl butyrals haveproven particularly useful.

It is manifest that many resins may be employed and that it is notfeasible to recite herein all possible resins and combinations of resinswhich are useful for the purposes outlined. As stated hereinbefore, theusable group of resins includes those which display abrasion resistance,resistance to oils and greases, good aging characteristics andavailability in aqueous dispersions with relatively small resin particlesize. The resin or resins should also be inherently flexible or subjectto being made flexible by means of a chemically combined or otherwiseimmobile plasticizer. In addition, the resin should be thermo-plastic,or be subject to fusing or curing at temperatures of 300 F. or below.

. A detailed description of one specific form of the process of treatingleather is recited hereinbelow, it being pointed out that the process issubject to conventional variation at several points.

The leather, cut to strips of the desired Width and thickness issaturated with the water dispersion of resin, desirably by totalimmersion in the body of treating liquids. The leather should beagitated only long enough to Wet both sides and then allowed to soak inthe resin dispersion. Vegetable-tanned leather requires only about threeto five minutes soaking, while chrome- Specific gravity (resin) tannedleather may desirably be left immersed for some r weight.

Concentration of Dry Resin Con- Resin Bath tent of Treated (PercentResin Leather (Percent, Solids) based on original Drying of the resinsaturated leather can be accomplished at any air temperature up toaround 180 F. without damaging the leather. It has been found desirable,however, to dry the leather not only under con- 6. trolled temperatureconditions, but also under controlled conditions of humidity.

Following removal of the excess resin from the leather strips, thelatter are desirably mounted upon suitable supports to minimizeshrinkage, and are placed in a drying compartment which may be of theforced draft type having humidity control. The leather is dried for aperiod of time, for instance 4 hours, at a temperature of approximately100 to 125 F., with a relative humidity of to At the end of this initialdrying period, the humidity is allowed to gradually decrease to 50 to60% relative, and the drying is continued for a second suitable period,desirably of 4 hours. Following the second drying period, the humidityis allowed to drop to 30 to 40 percent relative, which often is theapproximate humidity range of the outside air, and the drying at thetemperature of to F. is continued for a third period of several hours,for instance a period of four hours length.

Following the drying step, it is desirable that the leather be subjectedto a resin fusing or curing step as Well as a pressure rolling step.While the latter two steps may be carried out in any desired order, ithas been found preferable to fuse the resin first and then to carry outthe rolling operation.

The fusing or curing step may be completed at a low temperature, forinstance 120 F., applied approximately for a period of one hour, atintermediate temperatures for shorter periods, for instance, F. for fiveminutes, or by higher temperatures, for instance 225 to 300 F., appliedfor 50 to 60 seconds, depending upon the temperature employed. Theapplication of pressure during the curing step is advantageous, and goodresults have been obtained by pressing the leather in an automaticelectric iron at a temperature of 225 F., the leather being subjected tothe heat and pressure of the iron for 15 seconds on each side.

' Following the curing, the leather strip, while still hot from thecuring step is passed between two metallic squeeze rolls to reduce theleather to uniform thickness throughout and to compress any strips thatmay have plumped during the soaking and drying steps. By spacing thesqueeze rolls the proper distance apart, the treated leather strips maybe made more uniform in thickness than they were before commencing thetreating operation.

It has been determined that vegetable-tanned leather tends to plumpduring the process while chrome-tanned leather tends to shrink. Bothtypes of leather may exhibit both phenomena, but each tends to theparticular shortcoming recited. Fast drying of the leather after resinsaturation exaggerates the shrinking and/ or plumping of the leather,and for this reason, the controlled drying of the saturated leather isthought to be important. Further, the rolling of the leather after thedrying step is most desirable in producing a uniform and consistentproduct of controlled dimensions.

The use of the treated leather in long draft spinning aprons provides avery important and beneficial result in that the size and quality of theyarn may be closely controlled over long periods of time. The uniformityin thickness as Well as the uniformity in apparent hardness orconsistency of the aprons is conducive to a uniform spinning operationand the production of yarn of uniform size and quality. In addition, theeven wear of the aprons in use, coupled with their greatly extendeduseful life, extends the time of this accurate quality control andassures retention of the control over long periods of time. So far as ispresently known, the useful life of the aprons and the length of timeover which they will afford good control of the yarn quality, will besubstantially equal to the actual physical life of the aprons. In otherwords, good control of the yarn size may be retained until the apronfails physically. In other types of aprons, this period of acceptableyarn quality control extends onlyuntil such time as the apron, throughdeterioration, causes production of a yarn of unacceptable quality. Froma physical viewpoint, such aprons might be capable of long-continuedoperation, but they would fail to produce yarn of the necessary quality.Hence, an important benefit of the invention is the long-continued andexcellent control over the quality of the yarn produced.

Various changes and modifications in the methods and products outlinedand disclosed herein may be made within the scope of the claims appendedhereto without departing from the spirit of the invention.

What we claim and desire to secure by Letters Patent is:

1. The method of treating leather including the steps of, impregnatingthe leather with an aqueous dispersion of a synthetic resin, anchoringthe leather to prevent shrinkage thereof, drying the impregnated leatherwhile so anchored, and subjecting the leather to heat to fuse the resinin the leather.

2. The method of treating leather including the steps of, impregnatingthe leather with an aqueous dispersion of a synthetic resin, drying theimpregnated leather, and subjecting the leather to heat to fuse theresin in the leather, and passing the leather through a pressure rollingstep.

3. The method of treating leather including the steps of, impregnatingthe leather with an aqueous dispersion of a synthetic resin, drying theimpregnated leather, and subjecting the leather to heat to fuse theresin in the leather, and passing the leather through a pressure rollingstep while the leather is still warm from the heating step. v -4. Themethod of treating leather including the steps of, incorporating from 1%to by weight of a synthetic resin into the leather by impregnating theleather with an aqueous dispersion of the synthetic resin, immobilizingthe leather to prevent shrinkage thereof, drying the impregnated leatherslowly in an atmosphere of decreasing humidity, and subjecting the driedleather to heat to fuse the resin in the leather.

5. The method of treating leather including the steps of, incorporatingfrom 1% to 10% by weight of a synthetic resin into the leather byimpregnating the leather with an aqueous dispersion of the syntheticresin, removing excess resin from the leather so as to leave the latterimpregnated with the aforesaid 1% to 10% resin concentrated at thejunctures and intersections of'the fibers of the leather, drying theimpregnated leather, and subjecting the leather to heat to fuse theresin in the leather in a multiplicity of small spaced bodies.

6. The method of treating leather including the steps of, incorporatingfrom 1% to 10% by weight of a synthetic resin into the leather byimpregnating the leather with an aqueous dispersion of the syntheticresin, removing excess resin from the leather by applying pressurethereto so as to leave the latter impregnated with the aforesaid 1% to10% resin concentrated at the junctures and intersections of the fibersof the leather, drying the impregnated leather, and subjecting theleather to heat to fuse the resin in the leather in a multiplicity ofsmall spaced bodies.

7. The method of treating leather including the steps of, impregnatingthe leather with an aqueous dispersion of a synthetic resin, expressingfrom the leather excess resin while the resin is still in aqueousdispersion, the

expressing being carried to a degree sufficient to leave the leatherwith a resin content of 1% to 10% by dry weight, drying the impregnatedleather, and subjecting the leather to heat to fuse the resin.

8. The method of treating leather including the steps of, impregnatingthe leather with an aqueous dispersion of a synthetic resin, expressingfrom the leather excess resin while the resin is still in aqueousdispersion, the expressing being carried to a degree sufficient to leavethe leather with a resin content of 1% to 10% by dry weight, drying theimpregnated leather, subjecting the leather to heat to fuse the resin,and passing the leather through a pressure application step while theresin is still plastic from the heating step.

References Cited inthe file of this patent I UNITED STATES PATENTS1,740,680 Burnham et al Dec. 24, 1929 2,272,057 Cheetham Feb. 3, 19422,356,879 Pense et al Aug. 29, 1944 2,452,536 Kirk Nov. 2, 19482,614,094 Wheelock Oct. 14, 1952 2,635,060 Cheronis et al. Apr. 14, 1953FOREIGN PATENTS 439,884 Great Britain Dec. 9, 1935

1. THE METHOD OF TREATING LEATHER INCLUDING THE STEPS OF, IMPREGNATINGTHE LEATHER WITH AN AQUEOUS DISPERSION. OF A SYNTHETIC RESIN, ANCHORINGTHE LEATHER TO PREVENT SHRINKAGE THEREOF, DRYING THE IMPREGNATED LEATHERWHILE SO ANCHORED, AND SUBJECTING THE LEATHER TO HEAT TO FUSE THE RESININ THE LEATHER.